Do statins reduce Alzheimer’s risk?

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Behind the Headlines

Tuesday August 28 2007

The “first direct evidence” that statins – cholesterol-lowering drugs – can reduce your risk of developing Alzheimer’s disease by 79% has been found, the Daily Mirror reported. Researchers discovered “fewer “tangles” – a conclusive sign of Alzheimer’s – in the brains of those who took the drug” the newspaper reported.

The story was based on a study that looked at the brains of people after they had died, and compared the findings between people who had taken statins and people who had not. The study authors caution against generalising these findings to a living population. The study looked only at brain changes that are known to be typical of Alzheimer’s disease, and not those that put people at risk of developing symptoms of Alzheimer’s disease.

The study cannot establish whether taking statins directly prevented these changes in the brain, as it cannot establish which event came first, statin use or the brain changes. In addition, many other factors could play a role in the development of these changes. Further studies are needed before it can be said for certain whether statin use reduces the risk of Alzheimer’s disease.

Where did the story come from?

Gail Li and colleagues at the University of Washington and other research and health care institutes in Washington carried out this research. The study was funded by the National Institute on Aging in the US and was published in the peer-reviewed medical journal, Neurology.

What kind of scientific study was this?

This cohort study looked at statin use in 110 people who had been enrolled in the large Adult Changes in Thought study between 1994 and 2002, and had since died. When they started the study, the people had been 65 years or above and had normal brain function; during the study, people were examined every two years to see whether they had developed Alzheimer’s disease (AD).

After they died, the volunteer’s brains were examined, to see if they showed the typical signs of Alzheimer’s disease: plaques and tangles in the brain. Researchers then looked back at prescription data to see which volunteers were statin users and which were not. Anyone who had received three or more prescriptions for 15 or more statin pills was considered to be a statin user. Researchers then compared how severe the plaques and tangles were in people who took statins and those who did not, using complex statistical methods. In these analyses they also took into account any differences in sex, brain function at baseline, age at death, brain weight, and the presence of small lesions in the brain.

What were the results of the study?

The researchers found that people who took statins were less likely to have typical Alzheimer’s disease like brain changes – plaques and tangles – than those who did not (the odds of having these changes were reduced by 79% – the number reported by the papers). When they looked at plaques and tangles separately, statin users were more likely to have less severe tangles, but not plaques, than people who did not take statins.

What interpretations did the researchers draw from these results?

Researchers concluded that there is an association between statin use and tangles at post-mortem, one typical feature of Alzheimer’s disease. They acknowledge that additional studies are needed to look at whether statins “may be” causing the reduction in the development of these tangles.

What does the NHS Knowledge Service make of this study?

This was an interesting preliminary study, but it has several limitations, which the authors acknowledge:

As the researchers could only look at brain pathology after death, they cannot say for certain whether the tangles and plaques developed before the volunteers started taking statins or after. Without knowing which event came first, it is impossible to say whether statins caused these changes in brain pathology.

As volunteers were not randomly allocated to statin use or non-use, these groups may not have been balanced in terms of their characteristics. In fact, more statin users were male, they had more cardiovascular disease, were more likely to be smokers, and had lower cognitive function scores at the start of the study. Although the researchers tried to adjust for these factors, these or other factors may be responsible for the reduction in Alzheimer’s disease pathology rather than statin use.

These findings relate to what the brain looks like after the volunteer has died. The authors do not report whether, in life, the volunteers had any symptoms of Alzheimer’s disease, therefore we cannot say whether statin use was associated with symptoms in living volunteers.

Those who agreed to post-mortem examination were a small subset of those in the study and this means these people were not representative of the entire population enrolled being studied. They were more likely to be female, Caucasian, and older at death than other volunteers. Therefore these findings may not be applicable to the population as a whole.

In light of these facts, the authors of the paper state that “our findings should be extrapolated to living populations with the greatest caution, if at all”.

Sir Muir Gray adds...

This is reassuring evidence that makes it very unlikely that taking statins can increase the risk of Alzheimer’s disease; whether they decrease the risk is a question that requires further research.